Process of separating bagasse pith and fiber



Nov. 8, 1955 c. BIRDSEYE PROCESS OF SEPARATING BAGASSE PITH AND FIBERFiled May 6, 1952 IN V EN TOR.

;III IIIIIIIIII United States Patent PROCESS OF SEPARATING BAGASSE PITHAND FIBER Clarence Birdseye, Gloucester, Mass., assiguor to Eleanor G.Birdseye, Gloucester, Mass.

Application May 6, 1952, Serial No. 286,237 1 Claim. (Cl. 92-1) Thisinvention relates to the manufacture of paper pulp from bagasse or otherstalks of the Grammae type. It comprises a novel process of separatingthe pith from the fiber of such vegetable material preparatory toconverting the pith-free fiber into paper pulp.

It is essential for the economical production of pulp from bagasse thatthe pith cells, which are more delicate and have dilferentcharatceristics from the fiber cells, should be separated so that thefiber may be treated in a substantially pith-free condition and notwhile contaminated or diluted with an extraneous substance.

As the bagasse leaves the last grinding mill in the sugar factory itresembles crushed corn stalks and is composed of about 40% pith and 60%bast fibers on a dry basis. The pieces of bagasse may be of any size orlength up to 6 or 8". Some of the pith cells are completely free of thefiber bundles and vice versa but in most cases pith is found clinging tothe fibers.

The process of the present invention comprises an optional dry siftingstep, a step in which the broken bagasse fibers are subjected to fluidpressure, a step of fractionating by pressure and friction, and anexplosive expansion of the compressed fiber mass. If desired the liquidingredients of the fiber mass may be removed in hot condition during thefractionating step and their latent energy recovered and utilized, andif desired the explosive expansion step may be followed by wet beatingof the fibers.

Going more into detail, the dry sifted pieces of bagasse are passed intoand through a confined space, such as a tube, wherein they are saturatedwith hot water or an aqueous solution and subjected to substantial fluidpressure. The hot saturated fiber mass is then compressed into a compactbody or plug and thus subjected to mechanical frictional fractionationwhich tends to separate pith from fiber and fiber from fiber.Subsequently, the compact body of the fiber mas-s is discharged atatmospheric pressure, whereupon the compressed vapor expands explosivelycausing further and adequate separation of the pith and fibers.

These and other features and characteristics of my novel process will bebest understood and appreciated from the following description of apreferred manner of carrymg it out with the assistance of apparatusshown in the ac companying drawings, in which the figure is adiagrammatic view of the apparatus with its various elements shown inflow sheet relation. 7

The dry sifting step may be carried out by feeding the broken bagasse toa rotary drum 10 having cylindrical perforated or mesh walls andequipped at its delivery end with vanes or lifts 11 which pick up thematerial and drop it upon a discharge chute 12. In this step the loosepith cells will pass through the walls of the drum while the fiber withsome adherent cells will be advanced for the next step of the process.

The dry-sifted bagasse fiber is directed by the chute 12 to a hopper 13having a pipe connection 14 by which hot water or any desired solutionmay be suplied to and mixed with the fiber as it passes downwardly inthe hopper to a screw conveyor 15. The conveyor has a power drivenhelical screw 16 which forcesv the fiber into a tube 17 through aconstricted section wherein the fiber is contacted mto a dense plug thatis effective to prevent flow back to a screw press 19. During 2,723,194Patented Nov. 8, 1955 into the hopper. A steam connection 18 leads tothe tube at a point beyond the constricted section and through thissteam at a pressure of 75 to 150 p. s. i. is admitted to the tube 17thereby saturating and subjecting the fiber to heat and substantialfluid pressure.

The saturated bagasse fiber is conveyed through the tube 17, which maybe of any convenient length and shape, this step the fiber bundles aresoftened and the bond of the pith cells to the fiber is weakened.

The screw press 19 is conical in shape and has a perforated inner wall20 enclosing a power driven helical screw 21. The bagasse fiber, stillunder the full tube pressure, is delivered to the upper end of the pressand forced downwardly again into a compressed plug at the dischargenozzle 22 of the press. In this compressing operation the fiber ismechanically kneaded and worked causing a partial separation of fiberfrom fiber as well as pith from fiber by friction between the movingfibers and between the fibers and the walls of the press.

During the pressing step the hot liquor that has permeated the fibers isforced out through the perforated wall 20 of the press, collected withinthe outer wall and drawn off by an outlet connection 23. The hot liquormay be utilized as a substantial source of energy at any convenientpoint in the system and if desired a limited amount may be led backthrough the pipe 14 to the hopper 13.

The screw 21 operates to force the compressed fiber plug progressivelyout through the nozzle 22 and in this step the fiber is suddenlyrelieved of pressure with the result that the contained vapor expandswith explosive force separating the fiber bundles into componentindividual fibers and substantially freeing them of pith cells.

The pith and fiber may now be segregated in any desired manner, as forexample, by that shown in my copending application Ser. No. 285,844filed May 3, 1952.

In the drawings a wet-beating step is suggested and for carrying outsuch a step a tank 24 is arranged to receive the fibers and pith cellsdischarged from the screw press. The tank is equipped with rotaryheaters 25 and with an overflow end fiber conveyor, not shown. The pithcells are carried off in the overflowing liquid and the now pith-freefibers are removed by the conveyor in condition for immediate use in thepreparation of paper pulp.

Having thus disclosed my invention and described in detail a preferredmanner of practicing it, I claim as new and desire to secure by LettersPatent:

The process of separating pith from the fibers of bagasse whichcomprises the steps of first dry-sifting the broken bagasse and therebyremoving loose pith cells from the fiber, advancing the sifted bagassefiber with adherent pith cells through a circuitous path while subjectedto steam pressure of to p. s. i., compressing the hot moist fiber into adense plug by mechanical pressure and thereby frictionally working thefibers upon each other and causing partial separation of those pithcells from the fibers that have been carried over from the dry siftingstep, explosively expanding the plug, wet beating the expanded productand removing the now freed pith cells by floatation.

References Cited in the file of this patent UNITED STATES PATENTS

